[ChromeDriver] Select the main frame if a non-existant child frame is targeted.

chrome/test/chromedriver/session.cc

Index: chrome/test/chromedriver/session.cc
diff --git a/chrome/test/chromedriver/session.cc b/chrome/test/chromedriver/session.cc
index 5313e51654b523430bba774e74fb7610684c710c..7169ca6a50fcda730e72434209e84da5e2e837e3 100644
--- a/chrome/test/chromedriver/session.cc
+++ b/chrome/test/chromedriver/session.cc
@@ -5,6 +5,7 @@
 #include "chrome/test/chromedriver/session.h"
 
 #include "chrome/test/chromedriver/chrome.h"
+#include "chrome/test/chromedriver/status.h"
 
 Session::Session(const std::string& id)
     : id(id), mouse_position(0, 0), implicit_wait(0), page_load_timeout(0),
@@ -16,6 +17,18 @@ Session::Session(const std::string& id, scoped_ptr<Chrome> chrome)
 
 Session::~Session() {}
 
+Status Session::WaitForPendingNavigations() {
+  if (!chrome)
+    return Status(kOk);
+  std::string full_frame_id(frame);
+  if (full_frame_id == "") {
+    Status status = chrome->GetMainFrame(&full_frame_id);
+    if (status.IsError())
+      return status;
+  }
+  return chrome->WaitForPendingNavigations(full_frame_id);
+}
+
 SessionAccessorImpl::SessionAccessorImpl(scoped_ptr<Session> session)
     : session_(session.Pass()) {}